Edexcel Jan 2013 Paper 3 Q4 (with explained solutions) |

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Edexcel Jan 2013 Paper 3 Q4

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4 The procedure below can be used to make 1-bromobutane. 1. Place a mixture of water, sodium bromide and butan-1-ol in a round- bottomed flask. 2. Slowly add a suitable volume of concentrated sulfuric acid to this mixture whilst it is also shaken and cooled. 3. When this addition is complete, heat the mixture under reflux for about 45 minutes. 4. Rearrange the apparatus for distillation and distil off the crude 1-bromobutane, collecting the distillate between 95and 105 C. 5. Shake the 1-bromobutane first with water, then with dilute sodium carbonate solution. 6. Separate the 1-bromobutane from the aqueous layer, add some anhydrous calcium chloride and leave the mixture to stand. 7. Decant the 1-bromobutane from the calcium chloride. (a) (i) Explain why sodium bromide and sulfuric acid are required in step 2. (1)(ii) What would be the effect on this preparation if concentrated sulfuric acid was added in step 2 without water having been added in step 1? Justify your answer. (2)(b) Explain why the acid must be added slowly and with cooling in step 2. (1)14 *P41216A01416*<br />
(c) Draw a labelled diagram of the apparatus that could be used to carry out the distillation in step 4. (d) Explain why the 1-bromobutane is shaken with sodium carbonate solution in step 5. (4) (1)(e) What is the purpose of the calcium chloride in step 6? (1)(f) Suggest how you would obtain pure 1-bromobutane after step 7. (1)(Total for Question 4 = 11 marks) TOTAL FOR PAPER = 50 MARKS *P41216A01516* 15<br />

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$Mark Mark Reject Acceptable Answers (The mixture) generates HBr (which attacks the alcohol) OR the alcohol must be protonated for the bromide ion to attack it successfully Acceptable Answers Reject The yield would be lower (1) Allow no 1-bromobutane made. Because bromine/Br2 would be formed/less HBr would be formed (1) Formation of alkene (by dehydration reaction) (1) Any two from the above three answers. Acceptable answers EITHER Dilution of sulfuric acid is exothermic/ reaction (of sulfuric acid with water) is (very) exothermic. OR would cause loss of volatile organics. Ignore the reaction is vigorous. Bromide is reduced to bromine. Mark Reject Reaction is explosive. Just acid is corrosive/ dangerous/causes frothing. Question Number 4a(i) Question Number 4a(ii) Question Number 4b<br /> ` Question Number 4c Acceptable answers Reject Mark Round-bottomed/pear-shaped flask (and contents) and heat/mantle/water bath (1) Still-head with stoppered thermometer opposite opening to condenser (1) Condenser with water flowing up(1) Collection of product from an unsealed apparatus either as shown or from a delivery tube into a flask/beaker or straight from the condenser into flask/beaker. (1) Allow continuous apparatus without joints. Acceptable Answers Reject Mark Removes/neutralizes acid/HBr Allow neutralizes sulfuric acid. Just react with acid Removes HCl Acceptable Answers Reject Drying agent/To dry 1-bromobutane / Absorbs any water present/To remove water. Dehydrating agent Removes excess water. Acceptable answers (Re-)distillation (over a narrow range either side of its boiling temperature/at its boiling temperature). Allow fractional distillation. Reject Stated temperature range of 95 - 105C or all other values outside of this range. Mark Mark Total = 11 Marks QUESTION PAPER TOTAL = 50 MARKS Question Number 4d Question Number 4e Question Number 4f<br />$

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